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Old 20th June 2003, 12:11   #1
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Net Audio Quad 33/303 upgrade

For some reason, I can't update the original report on high.fidelity.tk, so, for the final report, I moved it over here. This is the whole thing, blow by blow, in chronological order.

Wednesday, December 04, 2002

I have had a Quad 33/303 since 1981. It has performed flawlessly in all that time, and it remains the heart of No.2 system down in the basement (being supplanted by the all-Linn active system upstairs). In fact, it gets listened to more than No.1, as I go there to get a bit of peace and quiet and to avoid bothering the family, who don't like my taste in music (thus also the Grado headphone/Solo headphone amplifiers). The thought ot it being upgradeable was therefore appealing.

The upgrades were supplied by a small company Net Audio - read all about them at


My first foray was to the 303 upgrade. This is a replacement of the 303's power supply board, got at from underneath by taking off the cover plate and soldering the new one in place of the old. And, yes indeed, it made a difference. People who have read my posts here and on the HFC Forum will be aware that I am the least golden-eared person on the planet - "Tones the unbeliever" as cableman Bob ("Frontfloater") once characterised me. Subtle changes are no good, I have to be hit over the head with them. And this one did. Suddenly, there was bass there that hadn't been there previously. That's the thing that jumped out at me most of all. So for this one, definitely five stars. £45 well spent.

This encouraged me to go one better and get the 33 upgrade. This is a lot more involved, and at nearly £155 a whole lot more expensive. It involves replacing all the plug-in boards in the 33, the two amplifier boards inside the case and the disc and tape boards that plug in from outside. There is also an external power supply, operating through a connector on the tape board. And the difference I noticed was none at all. I ended up taking the case off the 33 and replacing the boards one by one (two by two in the case of the amplifier boards), to see whether there was a difference. There wasn't. Now it might well be that these things require running in, and that mine isn't run in yet, so my rating of zero stars out of five for this upgrade has to be seen in this light. If I find a difference with time, I'll amend this rating. It hasn't made things any worse, but the object was to improve matters! As yet, it hasn't.

This upgrade has another annoying feature - it takes quite a while to warm up. The old 33 was up and running instantly. This upgraded version takes a couple of minutes to get going. It gave me a fright the first time I heard it, with one channel sounding very muffled or cutting out completely. Just as you start thinking of expensive repair bills, it comes on song and all as it was before. I have had to learn to switch on the 33 some minutes before I listen.

So, on average for the whole packet, 2.5 stars, an excellent, cost-effective power amp upgrade dragged down by an expensive, non-working pre-amp upgrade. Further reports, if merited.

P.S. Qualification of something said in my initial report. The 33 mods take about 40 sec., not a couple of minutes, to come on song.

(Comment, 30 March 2003 - this was because I was doing something daft - I was expecting the outboard power supply to run the entire amplifier, 33 and 303, not just the pre-amp, and it couldn't. So I was plugging in the old mains connection to the 33 and this contributed to the problem. I now have a direct power connection for the 303, so all's well. But I do miss the cheerful Quad light on the 33 lighting up!)

2 February 2003.

Well, I thought, if it needs running in, it should be well and truly run in by now. So I took off the case and started playing music and changing boards. I became so good at this (even with the awkward Net Audio disc board, which is wider than the slot in the 33 and has to go in sideways and then be turned into position) that I feel that in any Quad 33 pitstop I could not be challenged! The test track was an old favourite, "I saw the light" by Chet Atkins and Jerry Reid. And did I hear a difference? Wellllllll, yes...I think. The Net Audio mods seemed to give a clearer,less muffled sound. More detail could be heard. Or was it because the Net Audio mods slightly boosted the volume (I was using a set volume of about 3.5 on the 33) and that always makes it appear as if there's more there? Unlike the 303 mod, which was "hit over the head" good, the 33 mod is much more subtle, but to a non-golden-eared person such as myself, so subtle that you have to ask yourself whether you're hearing a difference because you forked out £155 and you WANT to hear a difference. And if you have to do that, I think it's not worth the money. I would therefore promote the whole package from two-and-a-half stars to three. I wholeheartedly recommend the 303 mod to anyone who wants to improve their 303, but the 33 mod should be bought only by very perceptive folk who want to coax the very last bit of performance out of their 33.

9 February 2003

I reported to David Pritchard of Net Audio that his 33 upgrade didn't deliver the goods, and he's going to let me hear some other boards that he has. Watch This Space.

30 March 2003 (final report)

The modified boards have a type of capacitor by Sanyo, called "Oscon". (Pity the boards are inside, these are a particularly pretty shade of purple). These, according to David Pritchard, "improve detail and imaging". He put these on all four 33 boards, so off we went. And was it better? Weeeeelllllll...I think so. I didn't do my pitstop trick again, I just switched over to my 34/405-2, which is in the same setup. Previously, they sounded so alike to my ears that I had to look at the positions of the switches on the switch box, to find out which one was playing. They now sound slightly different. And David Pritchard is right; there does seem to be better detail and imaging, compared to the 34/405-2, but it's very slight, so slight that I wonder whether I'm kidding myself, because I want to hear the difference. So, for this particular, not particularly discriminating listener, the 33 mod is, as I said above, only for the discriminating listener who wants to squeeze the last milligram of performance out of his 33. For me, it's not worth the money.

(Final final report, 31 March 2003))

It would be remiss of me not to mention the completely contrary view to mine, held by someone much more knowledgeable than I. See the customer comments on the 33 mod. on Net Audio's website at

The man with the golden ear trumpet
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Old 3rd July 2003, 13:39   #2
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Hi tones. Is this Quad (303) by any chance in the same range as the 34/306? This is currently what I'm using and I find this amp surprisingly powerful though rated only at about 50 watts. Bought these about two years ago.

It's quite articulate also and I must say it even outguns bigger and higher rated amps. There are times when it can sound a bit forward, but it never losses its musicality. Sibilant vocals and badly recorded music with lots of high pitch notes though tend to show much and it could sometimes leave some ringing in the ears.

I'm just wondering though if an upgrade by the company you mentioned might do some wonders to my 306.

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Old 4th July 2003, 08:20   #3
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Hi, Osama, I'm not sure what you mean by "the same range", but the 33/303 combo is very different from the 34/306. You can see some of them here:


The Net Audio mods are made specifically for the 33 and 303 and probably wouldn't work in anything else (the 34 and 306 came along much later). However, people do tinker with Quad stuff, so try a search on Google. There's also a Yahoo! group for Quad devotees. It's dominated by fans of the valve Quad 22 amp (the immediate predecessor of the 33/303), but there's a lot of knowledge about all things Quad there. If I can find the address, I'll post it here.

I have my modified 33/303 and a standard 34/405-2 and I like them very much
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Old 4th July 2003, 11:44   #4
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Quad Yahoo group --> http://groups.yahoo.com/group/quadhifi

~I don’t suffer from insanity, I enjoy every minute of it~
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